Functional recovery from lesions in the escape system of the cockroach - II. Physiological recovery of the giant interneurons

1. The cellular basis of the behavioral correction of the cockroach's turning response was studied. 2. Intracellular recordings from cockroaches whose left cercus was ablated were obtained from the left and right giant interneurons (GI's) both before and after the period of behavioral recovery. 3. Five of the seven identified left GI's (no.'s 1, 2, 3, 5, and 6) significantly enhanced their responses to wind (Fig. 1 and 2). The other two (no.'s 4 and 7) did not change significantly (Fig. 2). 4. GI's 1, 2, 3, and 6 recovered about 25% of their normal responses. Their normal characteristic directional curves were well restored (Fig. 3). 5. The major, and possibly the only, source of sensory information to the recovered GI's was the right cercus (Fig. 4). 6. The responses of all the right GI's but one (no. 4) did not change (Fig. 5). Thus the normal left/ right balance of GI activity was partially restored. 7. The number of action potentials in the GI's after the period of behavioral recovery is sufficient to produce turning behavior similar to that of day 30 animals (Figs. 6 and 7). 8. The response latency of axons in the left connective relative to those in the right connective was also greatly improved (Fig. 8). Both the restoration of the balance between the number of action potentials in the left and the right connectives, and the improvement in the relative latency may cooperate in producing the behavioral recovery. 9. Synaptic events that could underlie these physiological changes are discussed.